1. Field of the Invention
The present invention relates to a fuel cell formed by stacking a membrane electrode assembly and a metal separator together. The membrane electrode assembly includes a pair of electrodes and an electrolyte membrane interposed between the electrodes.
2. Description of the Related Art
For example, a solid polymer electrolyte fuel cell employs a membrane electrode assembly (MEA) which includes an anode, a cathode, and an electrolyte membrane interposed between the anode and the cathode. The electrolyte membrane is a polymer ion exchange membrane. The membrane electrode assembly is sandwiched between a pair of separators. Normally, a plurality of fuel cells are stacked together, and used in stationary applications. Further, the fuel cells are mounted in a fuel cell vehicle, and used as an in-vehicle fuel cell system.
In the fuel cell, a fuel gas flow field (hereinafter also referred to as the reactant gas flow field) for supplying a fuel gas to the anode and an oxygen-containing gas flow field (hereinafter also referred to as the reactant gas flow field) for supplying an oxygen-containing gas to the cathode are provided in surfaces of separators. For each of power generation cells, or for every predetermined number of power generation cells, a coolant flow field for supplying a coolant is provided along electrode surfaces between the adjacent separators.
In the fuel cell of this type, in order to achieve the desired ion conductivity, the electrolyte membrane needs to be kept humidified. Therefore, the fuel cell adopts an approach where an oxygen-containing gas (e.g., the air) and a fuel gas (e.g., hydrogen gas) as reactant gases are humidified and the humidified reactant gases are supplied to the fuel cell.
In some cases, water for humidification is not be absorbed by the electrolyte membrane, and liquefied water is retained as stagnant water in the reactant gas flow field. Further, in the fuel cell, water is produced at the cathode by power generation reaction, and the produced water is diffused backward to the anode through the electrolyte membrane. Therefore, under the effect of the gravity, the water content tends to be condensed and retained at the lower end of the reactant gas flow field, and consequently, flooding of the condensed water may occur undesirably.
In this regard, as a fuel cell which is intended to make it possible to discharge gases effectively, and also discharge water efficiently, a solid polymer electrolyte fuel cell as disclosed in Japanese Patent No. 3123992 (hereinafter referred to as conventional technique 1) is known. As shown in FIG. 25, the fuel cell includes a frame body 1. A cell 2 and a cathode flow field plate 3 are fitted to one surface of the frame body 1, and an anode flow field plate 4 is fitted to the other surface of the frame body 1.
The cell 2 is formed by providing a cathode 2b and an anode 2c on a solid polymer electrolyte 2a. A plurality of cathode grooves 3a are formed on the cathode flow field plate 3, and a plurality of anode grooves 4a are formed on the anode flow field plate 4.
A pair of water inlet manifold holes 5a, a groove hole 5b connecting the water inlet manifold holes 5a to the anode grooves 4a, a pair of fuel gas inlet manifold holes 6a, and a groove hole 6b connecting the fuel gas inlet manifold holes 6a to the anode grooves 4a are formed on the upstream side of the frame body 1. A pair of fuel gas outlet manifold holes 7a, a groove hole 7b connecting the fuel gas outlet manifold holes 7a to the anode grooves 4a, a pair of water outlet manifold holes 8a, and a groove hole 8b connecting the water outlet manifold holes 8a to the anode grooves 4a are formed on the downstream side of the frame body 1.
The unconsumed fuel gas which has passed through the anode grooves 4a flows from the groove hole 7b through the fuel gas outlet manifold holes 7a to the outside of the fuel cell. Further, the water which has passed through the anode grooves 4a flows from the groove hole 8b through the water outlet manifold holes 8a to the outside of the cell.
However, in the conventional technique 1, the frame body 1 is elongated considerably along the flow direction of the fuel gas. Therefore, if the cathode grooves 3a are oriented horizontally, the height of the fuel cell becomes large as a whole, and in the case where the fuel cell is mounted in a vehicle, the space required for mounting the fuel cell is limited.
Moreover, water produced in power generation reaction is present in the cathode grooves 3a. The produced water moves downward in the direction of gravity, and the water may be retained as stagnant water. Consequently, the oxygen-containing gas may not be supplied sufficiently.
Further, in the fuel cell, metal separators may be used as separators. The metal separator is formed by corrugating a metal thin plate. A reactant gas flow field and a part of a coolant flow field are formed on the corrugated recesses (grooves) on front and back surfaces of the separator. The coolant flow field is formed by stacking grooves formed on the adjacent metal separators.
Further, a seal member is formed integrally with the metal separator for sealing the reactant gas flow fields, the coolant flow field or the like. At the outer periphery of the coolant flow field, grooves of the adjacent metal separators are stacked with each other. Therefore, gaps tend to be produced between the seal member and the outer periphery of the coolant flow field. As a result, the coolant may bypass the coolant flow field, and flow between the outer periphery of the coolant flow field and the seal members, i.e., so called shortcuts of the coolant may occur.
In this regard, for example, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2011-171222 (hereinafter referred to as conventional technique 2) is known. The conventional technique 2 relates to a fuel cell formed by stacking electrolyte electrode assemblies and rectangular metal separators together. Each of the electrolyte electrode assemblies includes a pair of electrodes and an electrolyte interposed between the electrodes. A coolant flow field is formed between the metal separators, around the electrode area for supplying a coolant in a longitudinal direction of the metal separators. At one end of the metal separators in the longitudinal direction, a pair of coolant supply passages are provided on both sides of the coolant flow field, and at the other end of the metal separators in the longitudinal direction, a pair of coolant discharge passages are provided on both sides of the coolant flow field.
The coolant flow field is formed between a plurality of corrugated ridges, and a blocking seal is provided for the coolant flow field. The blocking seal contacts a side portion of the corrugated ridge at the outermost position of the coolant flow field from the outside of the metal separator, and has a shape at least protruding in correspondence with part of the side portion having the corrugated shape.
According to the disclosure, with the simple structure, it is possible to suitably supply the coolant over the entire area of the coolant flow field, and shortcuts of the coolant can be prevented as much as possible.